Device for heat treatment of bulk materials

ABSTRACT

A mechanism for the cooling of bulk materials such as hot cement clinker emerging from a calcining furnace with a materials transfer device for receiving hot discharge from a furnace into the cooling mechanism with the cooling mechanism having a first cooling section with an immobile stepped grate inclined relative to the horizontal whereby material passes from a receiving end to a discharge end, also having a second cooling section positioned so that the material to be cooled is discharged from the first cooling section onto a receiving end of the second cooling section which includes a sliding grate, and a third cooling section having an immobile inclined stepped grate positioned to receive material from the discharge end of the second cooling section and passing the material over the third cooling section to a discharge end.

BACKGROUND OF THE INVENTION

The invention is directed to a device for the thermal treatment of bulkmaterials, particularly for cooling hot cement clinker emerging from acalcining furnace, comprising a materials transfer means arranged in theregion under the furnace discharge that can be charged with cooling gasand comprises a stepped grate inclined relative to the horizontal, thismaterials transfer means being followed by a grate such as, for example,a sliding grate that carries and conveys the material to be cooled.

Devices of this species are employed in the nonmetallic mineralsindustry in order to highly cool the material (for example, cementclinker or other mineral materials) previously calcined in a calciningfurnace immediately thereafter in the desired way. The red-hot materialcoming from the furnace discharge should experience an initial, greatcooling in a materials transfer means that can be charged with coolinggas and leads to the actual cooler, usually a sliding grate cooler,traveling grate cooler or the like, and should thereby be conveyed withoptimally good distribution to the following cooler on which the maincooling work is then performed while the material to be cooled continuesto be conveyed in longitudinal direction. At least the cooling air blownthrough the hot material in the materials transfer means shouldgenerally be reemployed or, respectively, employed in some other way inthe preceding furnace system as heated combustion air (secondary air,tertiary air).

In a known cooling means for cooling hot cement clinker (periodical"Zement-Kalk-Gips", No 2/95 pages 87-90), the materials transfer meanspreceding a conventional sliding grate cooler is composed of a singlestepped grate chargeable with pulsating cooling air whose angle ofinclination is smaller than the natural angle of slope of the hot cementclinker emerging from the calcining furnace, so that a layer of materialremains lying on the stepped grate on whose surface the fresh productmaterial to be cooled should slide in the direction to the conventionalgrate cooler. The fresh cement clinker bed should thereby also slide onthe single slope of the materials transfer means when the bed isadvanced on the following sliding grate cooler. However, one does notefficiently succeed in distributing the fresh clinker bed transverselyrelative to the main conveying direction as well with the knownmaterials transfer means; this would be necessary for a good heattransfer between the hot cement clinker and the cooling air. When thesole stepped grate of the known materials transfer means is fashionedextremely long, the risk is not precluded that the fresh clinker bed canno longer maintain itself on the stepped grate, which would result intoo low a clinker bed height, too short a dwell time of the cooling airin the clinker bed and the inadequate cooling thereof. Insofar as thesurface of the hot, fresh clinker bed were to crust due to inadequatecooling on a zone-by-zone basis, whereby incrustations at the surface ofthe bulk material would impede the passage of the cooling air, then theknown cooling means would make no provision therefor that suchincrustations are in turn destroyed immediately after they arise insofaras possible.

An object of the invention is to create a device of the speciesinitially cited having an improved materials transfer means that, givenlow technical outlay, enables an efficient distribution of materialtransversely relative to the conveying direction as well, enables areliable break-up of incrustations of material potentially forming onthe bed of bulk material and offers further advantages and that,finally, makes an increased heat recovery or, respectively, heatrecuperation from the clinker heat back into the furnace system and,thus, a further reduction in the specific heat requirement of an overallcement clinker production line possible.

FEATURES OF THE INVENTION

In the device of the invention, the materials transfer means is composedof three longitudinal sections between furnace discharge and the actualcooler, for instance sliding grate cooler, traveling-bar cooler, pipecooler or the like, the first of said three longitudinal sectionscomprising an immobile, inclined stepped grate, the middle sectionthereof comprising a sliding grate and the third section thereof againcomprising an immobile, inclined stepped grate, whereby all threesections are charged from below with cooling gas (usually, cooling air).The sliding grate of the materials transfer means situated in the middlesection is fashioned comparatively short and comprises up to five rowsof grate plates whereof at least one middle row of grate plates but notmore than three rows are movably arranged. The plane of thiscomparatively short sliding grate of the middle section of the materialstransfer means lies horizontally or is only slightly inclined inconveying direction. I.e., the sliding grate of the middle section onlylends the bulk material situated thereon a comparatively low conveyingspeed, as a result whereof the height of the product bed can be keptcomparatively great, this resulting in a long dwell time of the coolinggas in the product bed which, consequently, can cool well as a result ofthe cooling gas.

Whereas the stationary, inclined stepped grate of the first section ofthe materials transfer means of the device of the invention comprisesapproximately five through six steps or, respectively, rows of grateplates, the other inclined, stationary stepped grate of the thirdsection comprises only up to four steps or, respectively, rows of grateplates. Due to a high shoulder or, respectively, due to a high step, thestart of the stepped grate of this third section lies lower than the endof the short sliding grate of the middle section. A normal cooler,particularly a sliding grate cooler then follows the inclined steppedgrate of the third section of the materials transfer means. The shortsliding grate of the middle section can be expediently connected to thesliding drive unit of the normal sliding grate cooler following upon thethird section.

The advantage of the device of the invention is essentially comprisedtherein that, due to the arrangement of two immobile, inclined steppedgrates separated from one another and separated by the comparativelyshort sliding grate of the middle section, high bed heights and a goodtransverse distribution of the bulk material are enabled in order toimprove the heat transfer between the hot bulk material and the coolingair since a more reliable bank-up of the bulk material is achieved viathe two relatively short scarp distances separated from one another incombination with the intervening, short sliding grate. Given, bycontrast, a continuous stepped grate (for example, shown and describedin the afore-mentioned trade journal "Zement-Kalk-Gips") having anoverall length of the two stepped grates that are separated in thesubject matter of the invention, the desired, high bed height of thefresh, hot feed could not be achieved, since the necessary bankingeffect for the fresh material is lost over the long slope distance; thiswould lead to short dwell times of the cooling air in the product bed aswell as to a deteriorated heat transfer. In a single, long, continuous,inclined stepped grate in the materials transfer means, moreover,spherical accretions or, respectively, sintered chunks would roll downto the end of the slope. In the device of the invention, by contrast,these sintered chunks are decelerated in the middle section of thematerials transfer means on the practically planar surface of the bulkmaterial over the short sliding grate of this middle section and areslowly conveyed forward from this point.

In the device of the invention, the two immobile, inclined steppedgrates separated from one another in the materials transfer means areprotected against thermal and abrasive wear to the farthest-reachingextent because the angle of inclination of these two stepped grates issmaller than the natural slope angle of the bulk material, so that thebulk material remains lying on the two stepped grates in its cooledcondition below a defined parting line (shearing section) and acts as anautonomous anti-wear protection for the fresh bulk product materialsliding down thereover. Noteworthy wear of the grate plates shouldtherefore only be anticipated in the short sliding grate of the middlesection of the materials transfer means. In comparison to the grateplates of the immobile, inclined stepped grates, the grate platescontained therein are fashioned significantly simpler and they can alsobe more easily replaced, both having a cost-reducing effect.

The improvement in the distribution of the bulk material transverselyrelative to the conveying direction is essentially achieved with thetwo-fold bank-up effect of the two inclined stepped grates separatedfrom one another by avoiding too fast a flow-down of the banked, upper,fresh layer of bulk material in the main conveying direction, i.e. thetwo immobile, inclined, stepped grates separated from one another andnot having particularly great length or, respectively, the productlayers respectively remaining lying thereon are in the position tostabilize the upper layers of the bulk material.

The highest temperature of the fresh layer of bulk material, for examplered-hot cement clinker, will occur at the surface thereof. The particlesof material can frit or, respectively, adhere or, respectively, encrustthereat. Surface incrustations, however, would impede the passage ofcooling air and, thus, the cooling of the bulk material. Possibleincrustations on the surface of the bulk material are inventively brokenup at a sharp transition from the short sliding grate of the middlesection to the inclined stepped grate of the third longitudinal sectionin the device of the invention, forced by a high shoulder or,respectively, a high step between the end of the short sliding grate ofthe middle section and the beginning of the stepped grate of the thirdsection of the materials transfer means; as a result thereof, thenecessary air permeability is restored in the product layer to becooled.

The invention and further features and advantages thereof shall be setforth in greater detail with reference to the exemplary embodimentschematically shown in the drawing.

DESCRIPTION OF THE DRAWINGS

FIG. 1, the single FIGURE of the drawings is a schematic elevationalview of a cooling mechanism embodying the features of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawing schematically shows a longitudinal section through thedevice of the invention with reference to the example of cooling red-hotcement clinker discharged from a rotary tubular kiln. A materialstransfer means chargeable with cooling air from below is arranged in theregion below the kiln discharge, this materials transfer means beingjoined by a sliding grate cooler 10 of a standard type that carriers andconveys the material to be cooled. The materials transfer means issubdivided into three longitudinal sections (I, II, III) that areequipped with different grates. An immobile, inclined stepped grate 11is arranged in the first section I, having an angle of inclination of,for example, 20° that is smaller than the natural slope angle (α) of thefresh bulk material 12 (hot cement clinker) of, for example, 35°. Thestepped grate 11 of the first section I is followed in the secondsection II by a short sliding grate 13 at whose end 14 a furtherimmobile, inclined step grate 15 of section III follows via a high,downwardly leading step having the height h, the normal sliding gratecooler 10, finally, then following this stepped grate 15.

The arrangement of the two stepped grates 11 and 15 separated from oneanother enables high bed heights c of the fresh feed 12 in order toimprove the heat transfer, since a reliable back-up of the fresh feed 12is still achieved via the relatively short slope paths. Accretions andsintered chunks rolling down on the slope surface 16 of the bulkmaterial are decelerated on the flat surface 17 of the bulk material inthe middle section II of the materials transfer means and are slowlyconveyed forward from that point. Both stepped grates 11 and 15 areautonomously protected against thermal and abrasive wear since the bulkmaterial 12 is not moved below the dot-dash parting line or,respectively, shearing section and, in the cooled condition, remainslying on the stepped grates 11 and 15 as a permanent product bed 19.Wear of the grate plates is only to be anticipated in section II of theshort sliding grate 13. By comparison to the grate plates of the steppedgrates 11 and 15, the grate plates integrated therein are significantlysimpler and they can also be more easily replaced. An improvement in thedistribution of the fresh bulk material 12 transversely relative to theconveying direction 20 is essentially achieved with the two-fold back-upof material of the two stepped grates 11 and 15 separated from oneanother by avoiding too rapid a flow-off of the banked bed height havingthe height c. An additional transverse distribution of material is alsopromoted by the comparatively short sliding grate 13 of the middlesection II of the materials transfer means.

Possible incrustations on the surface 17 of the bulk material areeffectively broken up at the sharp transition 21 from the short slidinggrate 13 to the inclined stepped grate 15 and the necessary airpermeability of the product layer to be cooled is thus restored.

As also proceeds from the drawing, the distance b of the point ofintersection 22 between the dot-dash parting line 18 and the system line23 of the sliding grate 13 of the longitudinal section II from the end14 of the sliding grate 13 lies in the range a≧b≧0.5 a, whereby thedimension (a) corresponds to the width of a step 24 of the inclinedstepped grate 15 of the longitudinal section III.

When the device of the invention is employed as cooler for, for example,calcined ores, then, for example, a low-oxygen cooling gas can also beemployed instead of cooling air. Fundamentally, the device of theinvention can also be employed in apparatus for drying and/or burningbulk materials.

I claim:
 1. A mechanism for cooling bulk materials such as hot cementclinker emerging from a calcining furnace including a materials transferdevice for receiving a hot discharge from a furnace, the coolingmechanism comprising in combination:a first cooling section having animmobile stepped grate inclined relative to the horizontal having areceiving end for receiving hot material from a transfer device with thematerials passing over the stepped grate to a discharge for supportingsaid bulk material such that it has a slope surface at a first anglerelative to the horizontal; a second cooling section having a slidinggrate and having a receiving end positioned to receive material from thedischarge end of the stepped grate and having a discharge end so thatthe material moves from the receiving end to the discharge end saidsecond cooling section arranged so as to support said bulk material suchthat it has a surface at a second angle relative to the horizontal lessthan said first angle; a third cooling section having an immobileinclined stepped grate having a receiving end positioned to receivematerial from the discharge end of the sliding grate with the materialmoving to a discharge end for supporting said bulk material such that ithas a slope surface at a third angle to horizontal greater than saidsecond angle; and a fourth cooling section having a sliding grate with areceiving end and a discharge end with the receiving end positioned toreceive material from the discharge end of said third cooling section,said fourth cooling section arranged to support said bulk material suchthat it has a surface at a fourth angle relative to the horizontal lessthan said third angle.
 2. A mechanism for cooling bulk materials such ashot cement clinker emerging from a calcining furnace including amaterials transfer device for receiving a hot discharge from a furnace,the cooling mechanism constructed in accordance with claim 1:whereinsaid sliding grate of the second cooling section is comparatively shortin length from the receiving to the discharge end in comparison to thelength of the first cooling mechanism and includes up to five rows ofgrate plates; and at least one middle row of grate plates but not morethan three rows being movably constructed.
 3. A mechanism for coolingbulk materials such as hot cement clinker emerging from a calciningfurnace including a materials transfer device for receiving a hotdischarge from a furnace, the cooling mechanism constructed inaccordance with claim 1:wherein the sliding grate of the second coolingsection is horizontal or slightly inclined in the conveying directionwith an angle on the order of 3° or less.
 4. A mechanism for coolingbulk materials such as hot cement clinker emerging from a calciningfurnace including a materials transfer device for receiving a hotdischarge from a furnace, the cooling mechanism constructed inaccordance with claim 1:wherein the receiving end of the stepped grateof the third cooling section is at a lower elevation than the dischargeend of the sliding grate of the second cooling section and includes ashoulder.
 5. A mechanism for cooling bulk materials such as hot cementclinker emerging from a calcining furnace including a materials transferdevice for receiving a hot discharge from a furnace, the coolingmechanism constructed in accordance with claim 1:wherein the slidinggrate of the fourth cooling section has a sliding drive unit, and thesliding grate of the second section is connected to said sliding driveunit.
 6. A mechanism for cooling bulk materials such as hot cementclinker emerging from a calcining furnace including a materials transferdevice for receiving a hot discharge from a furnace, the coolingmechanism constructed in accordance with claim 1:wherein a=the width ofa first step of the stepped grate of the third cooling section at thereceiving end thereof; b=the distance between the point of intersectionof the parting line of material turning and flowing from the secondcooling section to the third cooling section and the distal end of thesliding grate; and wherein a≧b≧0.5 a.
 7. A mechanism for cooling bulkmaterials such as hot cement clinker emerging from a calcining furnaceincluding a materials transfer device for receiving a hot discharge froma furnace, the cooling mechanism constructed in accordance with claim1:wherein the receiving end of the stepped grate of the third coolingsection is dropped below the discharge end of the sliding grate of thesecond cooling section a distance to effectively break up the bulk ofmaterial so that the material is broken up and permeability of the layerof the material is restored.
 8. A mechanism for cooling bulk materialssuch as hot cement clinker emerging from a calcining furnace including amaterials transfer device for receiving a hot discharge from a furnace,the cooling mechanism constructed in accordance with claim 1:wherein thestepped grate of the first cooling section is formed having a steeperslope than the sliding grate of the second cooling section.
 9. Amechanism for cooling bulk materials such as hot cement clinker emergingfrom a calcining furnace including a materials transfer device forreceiving a hot discharge from a furnace, the cooling mechanismconstructed in accordance with claim 1:wherein the slope of the firststepped grate is smaller than the natural slope of fresh bulk material.10. A mechanism for cooling bulk materials such as hot cement clinkeremerging from a calcining furnace including a materials transfer devicefor receiving a hot discharge from a furnace, the cooling mechanismconstructed in accordance with claim 1:wherein the angle of inclinationof the slope of the first stepped grate is on the order of 20° with anatural slope of fresh bulk material being on the order of 35°.